Grinding tool



April 13, 1943 lK. l. HARVEY l2,316,161

GRINDING TOOL Filed May 25, 1939 lll M4 ATTORNEY.

u grit and the application.

Patented Apr. 13, 1943 UNITED STATES PATENT OFFICE 4- l 2,316,161 1 'y .y GRINDING 'rooL Kelsey I. Harvey, Beaver, Pa. Application May 2s, 1939, serial No. 275,174 e l (o1. rs1-e071 14 Claims.

This invention relates generally to abrading and more specically to abrading tools, their composition and the method of making the same.

The principal object of this invention is the provision of a novel abrading composition and the method of making the same.

Another object is the provision of an abrading composition having a metal reenforcing or supporting insert.

Another object is the provision `of a novel` abrading composition wherein the coefficient of the bond is such that `it will fracture during use,

thereby exposing the grit to produce faster and cooler abrading.

Another object is the provision of an abrading composition wherein the proportion of` thegrit n `materially exceeds that of thebond after it has been heat treated as compared with known types of abrading compositions known in the art.

A marked advantage is that this bonding comn `position may be used with any character of grit,

whereas other `bonds must be changed to suit the Another object is the provision of'a new and improved vitreous bond for unitingabrading f compositions. l

Another object is `the provision of a novel abrading composition that may be lformed, heat treated and cooled within a relatively short period of time in comparison with other brading compositions of this type known in the art.

Another object is the provision of a novel abrading composition that may be wetted for the purpose of application and immediately red to vitrication and rapidly cooled without injury thereto. l y

Another object is the provision of a novel `abrading composition that is capable of relatively high peripheral speeds in comparison with abrading compositionsof this type known in the art. l

Another object is the provision of an abrading composition that may be formed into a tool with metal embedded therein for reenforcing or supporting the tool and which may be heat treated without injury to the threads or` other relatively frailportions of the metal.

` `Other objects and advantages appear in the following description and claims. p

Innumerable abrasives have been used for many years, such as siliceous abrasives, sandstones, quartz, tripoli, pumice and volcanic dusts. These are relatively soft as compared with corundum, diamond, garnet and the artificial abrasives such as silicon carbide and fused alumina.

covery has led to an improved abrading composition as Well as to a new bond andrnds a` practical application in the art of abrading tools. i

One outstanding characteristic of this new bond is that it may be used with any of the abrasive grits without alterations, while in most every instance in the present art the bond is not only changed for different kinds of grits but for diierent sizes of the same grit, such as in the production of a softand hard abrading tool.

The preferred principal ingredients of the bond are boron, lead and lithium. The boron and the lead are preferably added in their oxide state and the lithium as `a carbonate, salt or in the form of lepidolite. Granulated or powdered borax vor boric acid have been found to be the best form for obtaining the boric oxide' because they are comparatively less expensive than other boron compounds and they provide the boron nits oxide form which is believed to provide the best results.

Lead monoxide or litharge has `been found to` silica alumina, potassium, fiuorine and a little potash together with some lime,magnesia, rubidium oxide, calcium oxide and manganese oxide.

The uorine in this mineral is also an active fluxihg agent and is believed to aid the fiuxing action of the lithium. This provides another reason for preferring the useof `lepidolite in place` of other lithium 'compounds such as the lithium salts. Fluorine may be substituted for lithium in the bond but lithium is preferable. i

One or more of the group including potassium,

sodium, calcium, magnesium, zinc and tin may be used individually in place of any one of the three principal ingredients in this ceramic. However, compounds of each of these elements add their singular characteristics to the composition, yet they all have about the same effect on the fusibility of the composition. Probably the most noticeable difference in the use of some of these substitutes is that they tend to make it more brittle. In some applications this may be highly desirable, whereas in others it may be preferable to maintain a softer product. Titanium, zirconium, cobalt, copper and barium have the effect of tempering the product. Some of these are too expensive to use commercially, especially in VieW of the beneficial results obtained with boric acid, ltharge and lepidolite -which are relatively cheap. However copper and barium are easily obtainable. They may be used as a substitute for one of the ingredients or they may be used in addition thereto for tempering the composition. Barium nitrate is also effective when added in the presence of lead, as the nitrate avoids` the formation of metallic lead during the melting if such diiiculty be experienced.

The three ingredients constituting the preferred composition of the bond, boric acid, litharge and lepidolite, were found to produce the best results when added in equal amounts by weight. However leachingredient may be used in proportions of to 60% by weight to obtain the bond. These proportions may be determined by using a triaxial diagram. If other compounds containing the chemicals boron, lead and lithium are used, their proportions may be determined by setting'up a triaxial diagram using thenew compounds or chemicals calculated to provide approximately by weight of boron, 16% by weight of lead and 6% -by Weight of lithium which represents the percentages of these elements when using equal proportions of boric acid, ltharge and lepidolite to make up the bond. The quantity of the substitutes for lead and lithium should be determined in the same manner.

The boric' acid, the lltharge and the lepidolite in powdered form are thoroughly mixed togethel. I

The size of the grit particles together with the relative grade of hardness of the tool may be determined by properly proportioning the amount of the bond of this invention to approximately the same percentages as those used by industries with the present types of bond well known in the art. The powdered bond with a sufficient amount of liquid to make it moldable, preferably water, is then added to the grit and thoroughly mixed to produce a homogeneous mass. The bond will hold the grit particles. together and it is generally unnecessary to add a temporary bond such as dextrine, glutrine, glycerine or other similar ingredients.

The batch is then placed pressed to form the tool.

If the tool being formed is relatively large in diameter and is made with a small size grit and has a low 'proportion of bond, such as approximately 3%, so as to produce a soft tool, then it has been found advantageous to apply heat to the tool to initially cure the same. This preliminary heat sinters the bond at a temperature as low as 150 F, and it hardens the tool sufficiently to enable it to be handled and transported to the place of nalheat treating. This feature is a very important advantage of this invention. If

in a mold and is a moderately sized tool, composed of approximately 10% or more bond, is being made, this preliminary heat treatment may be found unnecessary.

Abrasive tools may be made using from 3% to 95% by weight of bond with from 97% to 5% by Weight of grit or grit and a filler-grit. The filler being such as ground quartz or other suitable material which is equally substantially inert to the fluxing action of the bond but not having the abrasive qualities of the principal grit. kAn increase in the percentageof the bond in a mix increases the hardness of the tool to a point commonly referred to as the saturation point beyond which an additional percentage of the bond has the tendency to decrease the hardness or cutting efficiency of the tool. This saturation point is determined by the grit, shape and size, since the surface area of the grit, that must be covered by the bond, changes in proportion to its physical characteristics. Again this bond may be successfully employed for making tools having grit sizes ranging from 8 to 600 mesh.

After the tool has been removed from the mold it is ready for heat treatment. Any suitable heat controlled furnace or kiln may be used for heat treating the tool. The urnacemay be of the closed or opentype. However a vapor is formed during the heat treating process and it will coat any exposed metal parts with a vitreous deposit which is very hard and believed to be similar to the bond. Thus it is necessary to cover the exposed portion oi the metal inserts and any other metal in the furnace upon which it is not desired to have this vitreous coating.

A batch made up of the preferred compounds at the proportions given will sinter when heated 150 to 400 F. and becomes sticky and at aboutv 450 to 750 F. Vitrification is evident. A tool heat treated at approximately 750 F. completely vitrines in one to ve hours, depending upon its mass. However it is preferable to heat treat these tools to a temperature of approximately 1300L7 F. to 1600 F. and have them in the furnace from twenty minutes to about threehours, depending upon the mass of the tool.

' The temperature and the time during which it is applied is largely a matter of heat penetration and if the heat is applied locally within the mass it naturally is more effective relative to the time required to treat it. The tool may then be removed as a completely heat treated article. This temperature will not produce any harmful effects on the metal inserts which are preferably made of steel/andvv the tool will be thoroughly heat treated. The tool may be removed from the furnace even though it isa cherry red color without harmful effects and placed on a suitable rotary-machine Where any uneven or rough portions can be trimmed off, thereby trueing up the tool. Even before a tool has cooled to a degree Where it could not be touched by the hand it may be used for abrading purposes. These tools may be heat treated at temperatures as high as 2500 F. as the bond has a relatively long range of vitriiication without harming its structure but in such cases the tool should not have any metal inserts as they would burn and disintegrate.

If some of the elements in the above mentioned group are taken alone and used in place of lepidolite or litharge or other oxide compound, the mix will sinter at approximately 200 F. to 500 F. and the melting temperature is approximately 1000 F, to 1400 F. However the `substitution of these elements for boric acid produces a mix havingtemperature characteristics approaching that of the element added.

This bond thus provides a long `range of vitri- 1 fication. However when'on'e of theelements in-' cludingthe group of lithium, sodium, potassiun 1, Vv

calcium, manganese, tin,zinc"and fluorine are" used by themselves `as an 'ingredienti-in the mix they have the tendency of shortening the range of vitrication.

vitrify ata higher temperature such as approximately,` 1000"\F.-"andtheyimay quickly liquefy. Thus it may be preferable to use an oxide, carbonate or other similar forrnrather than the element,` dependingupon the `characterof the tool beingmade.A

The bond is tough and strong andcan withnally contain' a considerable'am'ount of oxygen and'iwater by weight which are given off 'during `the heat treating process the weight cfa tool after heat treatment is materially reduced and in some instances where thebond represents, a

small proportion of the tool it 'is diiilcult to seeit.`

This bond is very tough and strong and since the elements contained therein have high iluxing i They `may sinter at approxi-1 mately the same `temperature given above but Fig. `5 is a sectional view of a thin disk type tool with a metallic disk center.

Referring now -to Fig. 1 of the drawing, 10

represents a cutting tool having a steel core memi ber I I with hexagonally shaped flanges I2 spaced apart, forming an `annulargroove` I3 therebetween. The center 0f the core is bored out as 'indicated at I4 Vfor receiving a mandrel orishaft; The bore `rnayalso be threaded as illustrated .for

receiving a threaded mandrel. `I5 represents a reenforcing ring centrally `positioned in the wheel as it is being molded. i i

`In AFig.` 2 a disk` type` of grinding' tool I6 is 4 shown wherein hexagonal nuts I1 are inserted in 1 stand severe thermal shocks. Owing to the fact `that the ingredients making up this bond origicharacteristics it isbelieved" to dissolve a small portion of the surface andthe matrix of the grit as it vitrines,` therebyrnaking a very` strong union.

When used in abradingja small portion of the bondsurrounding a piece'ofgrit fractures and falls away,` leaving a sharp edge of the grit` lexposed.- When r,this sharp edge ofthe grit `wears down or breaksoff another` small portion of the bond fractures and fallsaway,exposing a new `sharp edge ofthe grit particle. Thisaction pro,-

duces cool'clean cutting tools. This is unlike other bonds which generallyrelease the whole `grit particles when they fracture or thebond merelyfwears away with theigrit.l ,i

Again the strength andftoughnessofthisbond permits aitool to be usedat 12,000 surface` feet per minute,` which is equivalent to the speed of tools made .up with,plasticbondssuch1 asfsynthetic resins and rubber. ,Tools have been rotated to produce a speed as high as 16,000surface feet per minutewlthoutbreaking, whereas vitrifled tools known in the art are tested at 9,5000` surface feet a, minute and are not recommended tobe used above 7,500 surface feet a minute. It

spaced relation about the tool and exposed to the rear face thereof for mounting thetocl on a metal i diskby means of bolts The nuts I1 are preferably tapered on one face as illustratedfat I8 so that they will resist being pulled` from vthe sock;r

ets formed in the tool. Serrations may be formed on the surface of these metal inserts, thereby increasing their dislodging resistance.

.Thersemi-spherically shapedtool IQshOWn in Fig. 3 is provided with ahexagon shapedcore 20, similar to that shown in Fig. 1 at II, with a series of spokes`2| radiating therefrom and are coni nected at their outer ends by a continuous rim 22 forming a wheel. This metal insertv may be made up inany desired"manner.` However it has been formed by welding the individual `pieces to- I `gether toform an integral structure.

Fig. 4` illustrates a'small cylindrical tool 23 having an octagonally shaped threaded core 24 tions are incalculable.

with a plurality of annular. grooves 25.

In Fig.,5 the disk type tool 26 is provided with a metalA disk 2`I`wl1ichis substantially as thin as` the abrading compound on each side thereof. The metaldisk is preferably made integralwith the metal core 2B. ln this manner a lai-ge diameter tool may be made up with a very fine grit in a vitreous bonding abradingcompound.

The shape of theselmounting and reenforcing inserts maybe formed to. best for which the tool is intended and their limita- However this im proved abrading compositioncprovides avtreous bond which 4surpasses other abrading tools of similar character and permits the use of metal inserts which cannot be embodied inl toolsr requiringheat treatment at temperatures at which metals, such i as steel; are impaired or become distorted. Again has been proven that these wheels may besafely f operated at speeds equivalent to and greater than the speeds recommended for tools made with bonds comprising synthetic resins and rubber and their cool clean cutting action is maintained.

In the accompanying drawings practical embodiments illustrating the Vprinciples of this in-V vention are shown wherein:

Fig. 1 is a sectional viewshowing a grinding tool having a steel reenforcing ring embedded therein;

Fig; 2 is a. sectional view of a grindingtool of the disk type which may be mounted by means of, independent nuts embedded in the tool and exposedon the rear face thereof.

Fig.,3is a sectional view oi a spherically shaped grinding surfacetool having a reenforcing wheel formed integral with the threaded hub.

`Fig.` `4 is a sectional view of a small grinding tool showing a threaded metal insert in the axial center` adjacent one end thereof for mounting the same.

this sameA abrading composition may be heat treated at higher temperatures, in which case the metal inserts are omitted, without detracting from vthe abrading characteristics and without requiringthe slow cooling or annealing of the tools for periods of ten days to three weeks, as in the present practice.

In ruling the molds the material is preferamy `introduced in a whirling or spinning manner.

y third of its weight upon vitrication.

Thus when the tool is pressed there is sulicient bulk in the bond to provide green strength and after heat treatment the bond having been materially reduced provides a coolfree cutting tool open in structure.

serve the purpose the open porosity of the tool may be determined.

This process may be advantageously employed in place of the use of fillers for regulating the density in a tool. It alsoy provides a-method for obtaining tools of greater density with the use of materially reduced pressures.

I claim:

1. An abrasive article vconsisting of abrasivel particles bonded with' a ceramic derived of a boron salt, a lead salt and a lithium salt.

2. An abrasive article consisting of abrasive grains4 bonded with a ceramic composition consisting of a boron salt, a lead salt and a lithium salt, wherein the boron and lead were initially approximately from 4 to 30 percent by weight of the salt and the lithium from 1.5 to 11 percent by weight of the salt.`

3. An abrasive article consisting by weight of from 70 to k97 percent of an abrasive material bonded with a fused ceramic composition initially by weight of from 30 to 3 percent, the ceramic bondconsisting of a-boron salt, a lead salt and a lithium salt, wherein the boron and lead were initiallyl approximately from 4 to 30 percent by Weight of the salt and the lithium from 1.5 to 11 percent by weight of thesalt.

4. An abrasive article consisting by weight of from 97 toy 5 percent of an abrasive grit and a grit 1111er bonded with a fused ceramicI composition initially by weight di from 3 to 95 percent,

, the ceramic bond consisting of a boron salt, a lead salt and ak lithium salt, wherein the boron and lead were initially approximately from 4 to 30 percent by weight of the salt and lithium from 1.5 to 11 percent by weight of thesalt.

5. An abrasive article consisting' of abrasive particles bondedwith a complex ceramic ccn-y taining substantial proportions` of boron, lead and lithium substances.

6. An abrasive charge for the production of abrasive articles consisting of abrasive particles. and a complex ceramic bond of 10% to 60% oi boron containing substance. 10% to 60% of lead i ceramic bond, of boron, lithium, and a substance weight of abrasive particles bonded with .9% to containing substance, and 10% to 60% of lithium containing substance. 1

7. An abrasive charge for the production of abrasive articles consisting of abrasive particles, and a vcomplex ceramic bond of boric oxide, lead oxide, and a'lithium containing substance initially in approximately equal proportions.

8. An abrasive article consisting of abrasive particlesbonded with a ceramic containing substantial proportions of boron, lead, lithium and a substance containing one of a group consisting of potassium, sodium, calcium, magnesium, zinc and tin.

9. An abrasive'article consisting of abrasive particles bonded with a ceramic containing substantial proportions ofboron, lithium and a sub.' stance containing one of a group consisting of potassium, sodium, calcium, magnesium, zinc and tin. l.

1K0. An abrasive article consisting of abrasive particles bonded with a ceramic containing substantial proportions of lead, a lithium and a substance containinglone of ka group consisting of potassium, sodium, calcium, magnesium, zinc and tin.

l1. An abrasive article consisting of '70% to 99.1% abrasive particles and 30% to .9% of a containing'one of a group consisting of potassium, sodium, calcium, magnesium, zinc and tin.

l2. An abrasive-article of the character described consisting of abrasive particles and a ceramic bond comprising boron, lead, lithium substances, in proportions approximately'providing 15 parts by weight of boron, 16 parts by weight of lead, and 6 parts by weightof lithium.

13. An abrasive article of the character described consisting of abrasive particles bonded with a fused vitreous ceramic containing substantial proportions of boron, lead and lithium substances and havinga metallic insert therein held in the article by the ceramic bond.

1K4. An abrasive article ofthe character described consisting of from 99.1% to 28.7% by '71,3% by weight of fused vitreous ceramic containing substantial proportions of'boron, lead and lithium substances.

- KELSEY I. HARVEY. 

